Investigation With Impact Echo


When investigating defects and deficiencies in concrete you need all the information you can gather.

It would be a nice benefit if you could just drill and extract core samples from every part of your element.  Pull 50-100-500 cores from every corner; a thousand would be even better.  No matter the time it would take.  Although this task would be immensely beneficial, it would be ridiculous to "swiss cheese" the member and an extremely an unlikely option anyway.  But consider this...

With Impact Echo, Tecvac, Inc. can produce a color coded grid map depicting the condition of 20,000sf of concrete, with simulated core extractions 5'o.c., in just three days.

Impact Echo Technology utilizes an extremely advanced method of non-destructive testing that will provide the necessary background data for assistance in making the right decisions to prepare an optimum repair strategy.  Here are just a few of the common applications Tecvac technicians have performed:

• Delamination surveys of fascia tile tunnel walls
• Sandwiched membrane integrity
• Internal crack, void and honeycombing 
• Surface opening crack depth measurement
• Debonding of topping slabs
• Slab thickness measurement
• Injection repair quality
• Reinforcing debonding

The DOCter^tm (Defect Orientation Confirmation Tester) introduces a short duration stress pulse into the test object by technical impact on the surface.  A compression wave then travels into the object and is reflected by internal defects or external boundaries.  The wave propagates back to the surface and again into the test object by which a transient resonance condition is set up as multiple reflections occur.  This information is picked up by a transducer placed close to the impact point, processed and presented in graphic form.

This is a core sample from a bridge member surveyed in Georgia.  Just a fine little crack, seemingly unimportant from a glance.  Technicians however, were receiving information graphs of something totally different.  Repeated shots at and near the crack produced the same results...here is what they found through a confirmation core from that location:

Just beneath the surface was severe honeycombing attributable to poor consolidation.  At the rear end of the core there is a piece of embedded form wood.   

This condition would have been totally overlooked with an observational survey and recording.  Any repair proposed would have no doubt entailed a simple injection of the crack; which would have failed in a short period and caused a re-repair.  Impact Echo finds internal defects that cause surface defects; proper analysis leads to a proper repair. 

Each of our technicians are carefully trained in the use of Impact-Echo.  I was trained at Cornell University by the inventor over 20 years ago, when there were only two of these machines in the whole of the United States.  Our technicians performed the most extensive Impact-Echo survey ever performed in Taipei, Taiwan for the Dept. of Rapid Transit Systems on their MUTA Line.

If you want to get closer to the root of the problem...Call Tecvac, Inc.  We offer short notice world-wide service to support your efforts.

Office 703 742-9186  Toll Free 800 847-9324  

   

Debonded Topping Slabs and Delaminations

The conventional method of repairing debonding and delaminations is to remove and replace the defect.  Sometimes that can entail a huge problem for the installer or owner when its a bridge deck topping, or some other facility with a large amount of square yardage -like a parking garage.  Not only can the removal and replacement require a high degree of coordination efforts, the area most times has to be taken out of service which can severely impact revenue streams.

When the Washington Metropolitan Area Transit Authority was in the final stage of opening its Suitland Station, it discovered the 4" silica fume topping slab cast onto the structural slab, that was scheduled to receive a quarry tile finish, was spotted with a large number of delaminated areas.  Since the platform was demobilized of equipment, and was now a literal island, this condition posed a nightmare logistical problem to remove and replace the topping...and would severely impact the scheduled opening (revenue). Tecvac, Inc. identified and verifyably put back into composite some 4,500sf of delaminated topping in-situ using its exclusive TecBondtm Interface Permeation Process and allowed the finish tile work, and the opening, to proceed on schedule.

When heavy forklift equipment damaged/delaminated a 3" topping slab cast onto T- panels on a second story warehouse floor, the disruption necessary to commercial retail tenants below to accommodate any form of removal and replacement was foremost on the minds of the owner and the property manager.  At the very least, an R&R operation would necessitate vacating  the occupant tenant and all of the tenant businesses beneath the warehouse (125,000sf) to temporary off-site facilities.  Then, when the repair was complete, moving all the tenants back into their spaces.  A costly endeavor to say the least but, without some alternative, there was no choice; since the T-panel ceilings above the retail spaces would occasionally deposit concrete chunks on desks and equipment below.  Working at night, technicians identified (Impact Echo survey...more later on this non-destructive testing method) and verifyably re-bonded 35,000sf of delaminated area in just 20 days...independent pull tests broke in the substrate at over 200psi and the floor was verified safe with load testing.  Noteworthy, the operations did not necessitate the displacement of the occupant or a single tenant located below.

Tecvac, Inc. is a supplier of the TecBondtm Interface Permeation Process and other high quality advanced technology services to the concrete, masonry and stone repair industry.  Where revenue conservation and a quick turn-key repair is required, Call Tecvac, Inc. with your toughest problem.

Tecvac, Inc.

800 847-9324

www.tecvacinc.net

Crack Injection Without Surface Defacement

A good number of cracks in concrete, masonry and stone pose no structural threat to the member or the structure.  However, the mere sight of a crack in an overhead beam or support column will send the general public into an uneasy nervousness.  The repair of these cracks with conventional epoxy pressure injection might result in a repaired crack, but unless the completed repair is painted or coated, the resulting esthetics are often far worse than the crack itself.

Pressure injection requires the crack to be sealed with a material, usually a paste epoxy, that will tenaciously bond to the surface of the member being injected.  This tenacity is a requirement to contain the pressures exerted on the repair resin introduced into the fracture.  Removal of this sealer epoxy is most often performed by grinding the material off the surface with a rotary grinder; and most often mars the surface in such a way the defacing leaves little doubt a repair has been performed.  The removal of the crack sealing material can be impossible on fluted panels, decorative concrete, statues and historic members.  Depending on the severity of the cracking, or the "in your face" location of the crack, the fracture often leaves designers with little choice but to do nothing, or remove and replace the member.  Tecvac, Inc. has two solutions for this delima: CleanSettm and CrackMasktm. (Please visit our website at www.tecvacinc.net)

Repair of historic textured/aggregate concrete using CleanSettm.  After the repair is made, the proprietary setup materials just peel away. 

After restoring the fracture with CleanSettm, CrackMasktm was applied to the crack on the left.  Even close up, the repair and the original crack are hard to detect.

When there are cracks you need to repair and go away...choose Tecvac, Inc.'s exclusive CleanSettm and CrackMasktm Processes.

Tecvac, Inc.

800 847-9324

www.tecvacinc.net

  

Leaks Can Be A Difficult Problem To Resolve

Over the past 15 years, Tecvac, Inc. has performed some incredible feats; stopping water intrusion with its proprietary TecSealtm Permeation Leak Repair Process.  Here are some examples:

• Union Station DC - Chronic leaks plagued the station and a host of repair contractors spanning a seven year period could not get the water intrusion stopped.  At the occurrence of each rain event, management was forced to place large trash cans in front of public entrances to catch the water.  In 1999, Tecvac technicians stopped the water...and it is still stopped.
• Veterans Administration Headquarters Building - When the vast basement of this building was slated for finish-out to expand office areas, the area had leaked for over forty years.  To deal with the problem, sump pumps were installed in coffers and located every 50 feet to keep up with and remove the thousands of gallons of water ingressing.  Tecvac technicians had the entire area bone dry in just eight days.     
• Washington Metropolitan Area Transit Authority Traction Power Sub Station - The Eisenhower Avenue sub station was a utility complex that now houses massive electrical control boxes.  During the course of construction of the line system, the building received little attention.  By the time it was scheduled to receive equipment, the area had been ankle deep in water for two years.  One week and Tecvac technicians had it dry.  (even pulled off a repair to a 10 inch conduit with a failed seal.)
• Smithsonian's Hirshorn Museum - For years when it rained, public and office areas puddled water on the floors in various areas of the museum building.  There was a good idea where the water was coming in but, because of the buildings vicinity to the US Capitol Building, the building was an historic structure.  This status limited the methods and materials that could be used to make the repairs.  Tecvac technicians performed the repairs to the historic fabric of the building with it proprietary processes, stopped the water intrusion and did not breach the historic integrity of the exterior's exposed aggregate cladding.
• Ronald Regan International Airport Pedestrian Tunnel - A pedestrian tunnel connecting the parking garage to the main terminal required leak repairs...and a five year warranty.  After months of searching for a contractor who would offer such an extended warranty Tecvac, Inc. stepped up to the challenge.  Slab thickness, complicated with grade beams and varied contours, proved to be no match for TecSealtm.  The leaks were stopped and the warranty expired with no call back.
• Somerset Condominiums Balcony Leak - Year after year and contractor after contractor could not stop the water intrusion into the up-scale condominium.  Tecvac technicians solved the problem and repaired the leak in three days onsite.
• Dulles International People Mover Tunnel - When three other contractors all failed to stop the leaks with conventional urethane methods and materials, Tecvac, Inc. was given a week to perform in a "test" area.  Technicians exited the tunnel each day leaving a trail of dry cracks...eight months later the entire length of the tunnel was dry and ready for finish equipment.
• Just to name a few...  

When you have a difficult leak problem, call Tecvac, Inc. ....and get the results you are looking for.

800 847-9324

www.tecvacinc.net

Alkali Silica Reaction (ASR)

Our technicians have been mitigating Alkali Silica Reaction in concrete for over twenty years!  That's right...twenty years!

In June, 1993, Parsons Delew prepared a report of vacuum impregnation of Washington Metropolitan Area Transit Authority concrete platforms.  The report was presented at the American Public Transit Association's Rapid Transit Conference in Miami, Florida.  Here are some excerpts from that report:

• "Rehabilitation and retrofit of aged and distressed rail-transit structures and facilities often calls for unique and innovative engineering solutions, if the requirements of the operating-system safety and reliability, and the construction economy, are to be optimally realized…

• The concrete deterioration was caused by alkali-aggregate reaction and by the deicing salts, in conjunction with the freeze-thaw damage. The novel vacuum -impregnation method was used to successfully restore integrity of the affected concrete and thus obviate the need for platform demolition and reconstruction….

• The slab is cast in place using 3500psi concrete…In some instances the Minnesota Avenue structural slab had deteriorated to such an extent that the core recovery with sufficiently long pieces for compressive testing was not possible...

• In a generalized sense, only two basic options were available: Remove the defective concrete and repour, or utilize a procedure capable of in situ restoration of concrete…

• This method is based on first creating a partial vacuum in the concrete, a suitable polymer resin is then introduced into the concrete-matrix. The resin fills the cracks, including micro cracks down to 0.001 inch and less…

• Control cores were taken before and 8-hours after the completion of the impregnation operation. The cores were tested to yield a compressive strength ranging from 6,400 to 7,200 psi….

• The method was completely successful… 

• susceptibility of rebar to corrosion was also significantly diminished…

• The rehabilitated slabs are reported to be performing well."

Countless studies on ASR, from cause to prevention, have been performed.  A good number of the studies have concentrated on the mitigation within existing structures and individual members.  None of the studies (save vacuum impregnation) have presented a process or material that would -1. mitigate expansion, and -2. restore structural integrity.  The PermeNewaltm Permeation Impregnation Process does both. When you think your only alternative is demolition and replacement...think again.  Get a copy of the full report at www.tecvacinc.net.

                                                                    Tecvac, Inc.

800 847-9324

Why Vacuum Is Superior To Conventional Pressure Injection Techniques - Part 1

      The power of vacuum is not new.  Otto Von Guericke's demonstration of this power was performed on 8 May 1654 in front of the Reichstag and the Emperor Ferdinand III in Regensburg, Germany.  Thirty horses, in two teams of 15, could not separate the evacuated hemispheres until the valve was opened to release the vacuum. In 1656 he repeated the demonstration with 16 horses (2 teams of 8) in his hometown of Magdeburg, where he was mayor.  After the air was evacuated from the coupled 20 inch diameter half spears, atmospheric pressure held them together.  Considering Von Guerick got most of the air out, these spheres would have been held together with a force of 8-9000 lbf!
      Vacuum technoloy has been proving its merit in the repair of concrete, masonry and stone since the processes were patented the early 1970's.  While Tecvac, Inc. has not employed any horses in its efforts, we have been performing a variety of vacuum processes since 1991.  Many years prior to our conversion to vacuum, I would guess that we pressure injected as much epoxy as any of the other injection contractors in the area.  We know the difference vacuum makes in the permanence of repairs and there is no question about its unprecedented qualities, especially when coupled with the right repair resin.  We have vacuum applied epoxies and urethanes, but when performing structural repairs,  methyl methacrylate is our product of choice; and for good reasons.  Oh, I don’t suppose I blame the pressure advocates, especially those pump manufacturer's who's lively hood could be jeopardized with any notion that vacuum could un-do the prevalence of conventional pressure injection superiority.  Howbeit, it sort of reminds me of the buggy builder though, talking about Henry Ford.  No doubt, the guy had been building buggy's for 100 years and knew a thing or two about buggy's…, but he knew little about automobiles or Ford Motor Company.
Lets start with the basics and the propagation of vacuum's total superiority to conventional pressure injection.  As you might know, everything is porous.  A typical crack has fissures, voids and interconnecting cracks located in the side walls of the fracture.  These fissures, voids and interconnecting cracks continue on a microscopic level.  Imagine sealing and pressurizing one of these little voids with air …like a concrete balloon.  Is it hard to see how air and/or moisture can be trapped in the tiny fissures of the matrix?  Imagine filling the concrete balloon with a pressurized liquid.  How full do you think you would get it?  Yet, using only a modest 10in of vacuum would reduce the pressure inside the cavity by half.  But, lets just say we can only lower the pressure in the fracture area to 14psi from 14.7psi… and apply Boyle's Law.  One cubic inch, one cubic foot or 1 cubic meter of air will evacuate!  But vacuum, stand alone or assisted, employs the application of the most basic physics law...…You cant put two things in the same place at once.  Despite assertions otherwise, this is a very important law to be mindful of when considering vacuum vs. pressure.
      With that said, it has long been touted within the realm of pressure injection, and continues to be touted with numerous methods and apparatus to accommodate the purpose, that low pressure is better than high pressure.  Now, if vacuum will eliminate ALL pressure, how can it be said that vacuum cannot reasonably be considered useful?  That vacuum will contribute little, or be rarely useful to the pressure injection processes?  Doesn’t it make sense that this lower pressure zone, induced by vacuum, would be more receptive to resin installation?  Try the Boyle's Law thing.
The installation and penetration of the repair resin is hence, two different animals.  While pressure injection continuously labors against atmospheric pressure, vacuum injection flows because of atmospheric pressure.  Think about injecting at a very modest 25psi.  It is only serving its purpose by overcoming 14.7psi atmospheric (1bar).  Why would it take 100, 200 or 1000psi to move material in a fracture zone? Porosity?  Fluid resistance?  Why would a vacuum applied to the same set-up, the same fracture zone, pull the material into the fracture right out of an open bucket?...well, it does.  Vacuum injection is starkly adverse to pressure injection; the vacuum process actually de-pressurizes the repair resin and, naturally de-pressurizes the entire fracture zone.
      Yes, all concrete is porous.  The example of splashing a cup of water on a wall is evidence of that fact. However, while this porosity is remarkably useful when installing low-viscosity repair resins, it is not very useful when attempting to pressurize an enclosed fracture and then expecting the porosity of the concrete to dissipate entrapped air.  What is air entrained concrete?  More to the point, its not that concrete is good or bad at trapping air, it will tenaciously resist air moving through it.  Pick up a piece of the roughest open-surface concrete you can find, so thin its fragile to the touch, and try to blow air through it.  How much pressure do you think it would take to force air through a piece of solid concrete?  Our vacuum processes can seal a piece of plastic to a concrete surface so tight it is impossible to remove with out destroying it. How do we do that if air is moving through the concrete?  There is a profound difference in air and moisture vapor moving through a concrete matrix and the dissipation of pressurized air during an injection process.  I would pose this question to a competent and conscientious pressure technician…or pump manufacturer.

Why Vacuum Is Superior To Conventional Pressure Injection Techniques - Part 2

      Lets think about the little concrete balloon again; and lets say you have a respectable pressurized fill level of 85% at the point of refusal.  Good luck trying to get that concrete balloon 85% full without some exhaust.  Anyway, how would one propose to achieve 90% fill level?  Stay on the crack longer?  Lower the pressure? No!  It would require you to jack up the pressure.  Only makes sense doesn’t it?  Is it so hard for the pressure tout's to understand that increasing the pressure could, and will with enough force applied, extend the crack?  Why?  Because the entrapped air, the unvented void, will pressurize and exceed the strength of the matrix.  At what pressure the extension would transpire is directly related to the design strength and condition of the matrix.  Apply 3000psi pressure to a crack in a 2500psi matrix and it will give.  If the greatest advantage of high pressures is production, what is the greatest disadvantage?  And why do pressure injection specifications restrict the amount of pressure that may be applied during the injection process?
     We have used vacuum injection on just about all configurations of concrete, masonry and stone.  In addition to individual crack repairs, vacuum can repair spider/map cracking by the square foot instead of the conventional lineal foot basis.  Our vacuum processes can have an entire area repaired and back in service before a pressure application could be set up; and at a fraction of the cost.  Unlike pressure injection, vacuum injection can be safely used for the repair of an unrestrained element.  Topping slabs, mosaic tiles, delaminations, etc., can actually be simultaneously held together using the same vacuum forces used to perform the repair.  This notion that high pressure cannot "blow out" a crack is nonsense.  It is generally believed that any pressure in excess of 40psi has the potential to further damage concrete.  REMR Technical Note CS-MR-3.9 states, "The pressure used for injection must be carefully selected.  Increased pressure often does little to accelerate the rate of injection.  In fact, the use of excessive pressure can propagate the existing cracks, causing additional damage."  And what of ACI 301-05? "…pressure can propagate the existing cracks, causing additional damage."  Despite hollow preaching claims otherwise, the perils are real and well accepted.  The chance of further damage, propagation of the crack condition, is significantly increased by following conventional pressure injection methodology.
      Moreover, the matrix contains, at minimum, very nearly the same amount of moisture as the relative humidity of the atmosphere.  Oh I know about the water insensitive epoxies used for pressure injection. But, its back to that basic physics law when it comes to material penetrations, you cant put two things in the same place at once.  If there is moisture in the pore structure, there is moisture in the pore structure. Nothing will get in unless the moisture is displaced.  Pressure applied to the crack will not do it.  The flow and roll of the repair resin along the interior walls of the fracture may pull some of it out, but what happens to the moisture?  We have found that because a manufacturer says so, does not necessarily make it so. Most touted "water insensitive" epoxies will not bond when mixed with water.  The failure to bond issue that this causes has been explained by the pressure injection folks.  It doesn’t need to bond its been said.  They go on to explain the mere fact that the member has cracked indicates it has relieved the pressures exerted in the first place.  So, all one needs to do is fill the dormant void.  But what if the pressure is not relieved, and even if it is, what is the need to get the material so deep into the fracture?  Is 90% fill better than 70%?  Sure it is. Consider a crack only filled 80% full.  At the leading edge of the repair resin is a weakness.  Apply pressure and the crack will radiate from this unrestrained line and form a new fracture; that is, if the fracture is totally bonded the entire 80%. Of course, if its not bonded, the fracture will just open up again when/if it comes out of compression.  Many times my pressure injected crack looked fine, but six inches over, a new crack developed.  Coring of the existing repaired crack could reveal the new crack emanates from, and because of, the partially filled fracture.  There is little argument against "the more complete the fill, the more permanent the repair".
      Tecvac, Inc. routinely fills cracks as narrow as .001".  Moreover, there are petrographic reports from CTL Labs that indicate cracks as narrow as 5 microns wide being filled using vacuum technology.  We sometimes use pressure assist, but our success is directly attributable to our combination of vacuum and ultra-low viscosity repair materials, not pressure.  True, the technology and the repair resins we use are a bit more complicated, but its not brain surgery and, for the injection of typical in-depth cracks in concrete members, our prices are quite competitive.  Our repair resin of choice is low molecular weight methylmethacrylate (MMA).  This material shares all of the physical properties of epoxy, yet is just about as thin as water.  It has the ability to migrate into places epoxies will never see.  MMA has some drawbacks of course, but this material will outperform epoxy in every instance when it comes to injection.  It smells nasty, tends to bubble when put under pressure and is not easily metered.  So, there is obviously not a lot of enthusiasm from epoxy manufacturers or epoxy pump manufacturers.  But lets take the splash of water example again; splash a cup of water on a concrete wall or sidewalk.  See how the capillary action sucks the water deep into the matrix?  Now splash a cup of honey right next to it.  Very thin epoxies are claimed to be 40 centipoise, but most used for pressure injection approach 100 or better.  MMA is 5-7 centipoise.  See the difference?  Imagine the same two materials trying to get into that .001" wide fracture.  Pressure honey or vacuum water.  Oh, you have a crack that is 6" wide?  We can thicken MMA to paste if need be, and apply it at 20 degrees below zero.  Epoxy will not bond to epoxy.  Yet we can drill into/behind a shallow epoxy pressure injected crack, where the material only penetrated 1"¬2", pull our MMA up against and bond to the shallow epoxy filler; if its cured.  What do you do with shallow penetrated and improperly mixed epoxy?  A pin head of initiator in a 5 gallon bucket of MMA will fire!  We can remove our set up without grinding or marring the surface of the concrete.  ...The benefits of vacuum injection and its superiority over pressure injection go on and on.
     Witnessing these benefits, its not hard to understand why we, those of us in the vacuum injection industry, marvel at the natural wonder and the overwhelming power of vacuum.  We don’t expect pressure injection folks, and those with beneficial interest in that part of the concrete repair industry, to embrace, or even understand this technology.  However, we do understand pressure injection.  Tecvac technicians have performed 100's of gallons of pressure injected epoxy and know what it has to offer.  We are ready for any challenge and hopeful that the results would bring the pressure injection folks into the present.  The days of wooden wheels and buggy whips are a thing of the past.  But hey, if you think our "new fangled vacuum contraption" will get you killed, then ride on in your buggy...

Tecvac, Inc.

800 847-9324

www.tecvacinc.net